The present invention relates generally to a method for determining at least one characteristic of one or more security documents, and in particular to security documents including a sheet like substrate of plastics material and an opacifying layer, such as ink, applied to opposing faces of the substrate. The invention will be described with particular reference to a banknote, but it is to be understood, however, that the invention is not limited to that application.
Central and commercial banks currently devote significant resources to the handling of banknotes. For example, each time banknotes are returned to the banks, the banknotes are required to be counted, sorted for fitness for use, authenticated and sorted by denomination. Currently, both paper and polymer banknotes are counted by using currency verifying counting and sorting (CVCS) machines in most central banks. These machines are used to test for surface wear on each banknote, to detect the presence of counterfeit notes, to count the banknotes, to sort banknotes fit for future use from those unfit for future use, to bundle and wrap banknotes, as well as to destroy worn banknotes.
Various techniques are used in the CVCS machines for performing these functions. For example, the counting of banknotes is currently performed by mechanical apparatus which unfortunately produce considerable wear on the banknotes and are often are inaccurate. Surface wear on polymer banknotes is detected by scanning the banknotes to detect image fade effects in the printed designs formed in or on the opacifying layer applied to opposing faces of the banknote. Unfortunately, the performance of this technique, and many of the other techniques performed by the CVCS machines, requires the operation of complex and costly equipment, and is inherently inaccurate.
It would therefore be desirable to provide a method of determining at least one characteristic of one or more security documents, such as banknotes, which ameliorates or overcomes one or more disadvantages of the prior art.
The present invention provides a method of determining at least one characteristic of one or more security documents, such as banknotes, each security document including a sheet-like substrate of plastics material and opacifying layers applied to opposing faces of the substrate, the method comprising the steps of:
(a) projecting radiation from a radiation source into the substrate of each security document for propagation therein, the opacifying layers acting to guide the projecting radiation within the substrate;
(b) detecting a radiation emission of the substrate of each security document, the radiation emission resulting from the propagated radiation; and
(c) analysing one or more characteristics of the radiation emission.
In one embodiment, step (c) may include detecting the intensity of the radiation emission from said one or more security documents. Alternatively, or additionally, step (c) may include detecting the integrity of the radiation emission from said one or more security documents. The wavelength of the radiation emission may also be analysed in step (c).
The radiation emission may be detected in step (c) across at least part of the width of the security document.
In a further embodiment, the substrate may include a substance or material for modulating the propagated radiation within the substrate of each security document so that the radiation emission creates a machine readable effect, step (c) including detecting that machine readable effect. The radiation emission may include authenticating information which is detected in step (c). Conveniently, each substance or material so used may be denomination specific.
The projected radiation in step (a) may be projected onto an edge of the substrate of each security document.
Similarly, the radiation emission may be detected in step (b) from an edge of each security document. The edge from which the radiation emission is detected may be the same as, or different from, the edge onto which the projected radiation is projected.
In one embodiment of the invention, the opacifying layers only partially cover at least one of the faces of the substrate to leave an uncovered zone on that face, the projected radiation in step (a) being projected onto the uncovered zone.
The substrate may include material that acts to assist in the propagation of the radiation in the substrate. Such material may include fluorescent, phosphorescent, pearlescent or like inks.
One or more of the opacifying layers may be formed from ink. Alternatively, one or more of the opacifying layers may be formed from paper.
The radiation projected in step (a) may include visible light, ultraviolet light, radio waves or infrared light. The radiation projected in step (a) may form part of the visible or non-visible light spectrum.